Recently, needs for conducting cooling operation even in wintertime arises for cooling rooms such as a computer room in which the temperature is high through a whole year. However, when cooling operation is conducted by a normal air conditioner having only a heat pump, i.e. a compressor, under the condition that the temperature of the outdoor air is lower than the room temperature (hereinafter, referred to as low temperature cooling operation), drawbacks occurs. For example, a difference between high and low pressures of the refrigerant is not sufficiently generated, a limitation exists for lowering the rotation number of the compressor, or the operation efficiency deteriorates.
According to JP 2000-193327A (for example, FIG. 1), an air conditioning system, conducting normal cooling operation only by using a compressor and conducting the low temperature cooling operation only by using a liquid pump, is disclosed. Specifically, when conducting the normal cooling, an on-off valve of the compressor side is released and an on-off valve of the liquid pump side is closed. Consequently, the refrigerant is supplied only to the compressor side and thus the normal cooling is operated only by the compressor. On the other hand, when conducting the low temperature cooling operation, the on-off valve of the compressor side is closed and the on-off valve of the liquid pump is released. Consequently, the refrigerant is supplied only to the liquid pump side and thus the low temperature cooling operation is conducted only by the liquid pump. Generally, the power required for driving a liquid pump is approximately one tenth of that of the compressor.
In JP 2006-322617A, another type of air conditioning system is disclosed. Referring to FIG. 1 of JP 2006-322617A, the compressor is connected in series with the liquid pump. More specifically, the compressor, the outdoor heat exchanger, the outdoor expansion valve, the receiver, the liquid pump, the liquid flow connecting pipe, the indoor heat exchanger, and the indoor expansion valve are connected in the stated order, and an electromagnetic valve connects in parallel with the liquid pump. When conducting the cooling operation by the compressor, the electromagnetic valve is released and the refrigerant is not supplied to the liquid pump. In case that natural circulating operation is conducted when the temperature of the outdoor air is low, the electromagnetic valve is closed and the refrigerant is supplied to the liquid pump.
Further, another type of air conditioning system is disclosed in JP 2006-322617A. Referring to FIG. 4, the compressor is connected with the gas refrigerant side of the gas-liquid two phase receiver and the liquid pump is connected with the liquid refrigerant of the receiver, thus connecting the compressor in parallel with the liquid pump. Meanwhile, a circuit diagram of the overall system corresponding to FIG. 4 is not shown, and a circuit diagram and a control configuration used for operating the compressor and the liquid pump simultaneously are not disclosed in JP 2006-322617A.
In JP 2002-106986A, another type of air conditioning system, which selects the operating mode according to the temperature of the outdoor air during cooling operation, is disclosed. The cooling operation is conducted by operating one of the compressor and the liquid pump or operating the compressor and the liquid pump alternately. Further, another air conditioning system is disclosed in JP 2002-106986A, the air conditioning system includes a valve opening control means and a liquid pump rotation number controlling means for increasing the refrigerant flow circulated during the operation of the liquid pump.
Further, in association with detecting the liquid surface of the refrigerant in the accumulator, another type of air conditioning system is disclosed in JP H1-107071A. The air condition system includes an inlet pipe for supplying the refrigerant into the accumulator and further includes an outlet pipe and a bypass pipe. One end of the outlet pipe inserts into the accumulator and opens above the refrigerant liquid surface and the other end connects with a suction line of the compressor. One end of the bypass pipe opens on an inner wall surface of the accumulator and the other end thereof connects with the suction line of the compressor. A first heater and a temperature sensor are installed at the inlet pipe, and a second heater and a temperature sensor are installed at the bypass line. The air conditioning system estimates the level of the refrigerant liquid surface based on the first and second heater control and the detection results of the first and second temperature sensors.
According to JP H4-222366A, JP H8-49930A, and JP H8-296908A, another type of air conditioning system is disclosed. The air conditioning system estimates a level of the refrigerant liquid surface in the accumulator by using a sensor, such as an optical sensor, installed in the accumulator.
The air conditioning system disclosed in JP2000-193327A is configured so that the compressor, which mainly operates the cooling, is deactivated and the cooling operation is conducted only by the liquid pump during the low temperature cooling operation, thus improving cooling efficiency. On the other hand, when conducting the normal cooling operation, the liquid pump is not used. Therefore, the air conditioning system disclosed in JP2000-193327A has a drawback that value=function/cost is low.
The air conditioning system shown in FIG. 1 of JP 2006-322617A has a similar drawback as JP 2000-193327A. As described above, the overall circuit diagram, corresponding to the air conditioning system in which the compressor is connected in parallel with the liquid pump, is not disclosed in JP 2006-322617A. Further, the circuit diagram and the control configuration of the air conditioning system, operating the compressor and the liquid pump simultaneously, are not disclosed.
The air conditioning system disclosed in JP 2002-106986A has a similar drawback as JP 2000-193327A. Further, according to JP 2002-106986A, the air conditioning system increases the flow of the refrigerant circulating in the system at the time of the liquid pump operation. However, the liquid pump is operated without taking the degree of superheat and dryness of the refrigerant into account. Thus, limitation exists on the efficiency improvement.
The refrigerant liquid surface detection is configured redundantly in the air conditioning systems disclosed in JP H1-107071A, JP H4-222366A, JP H8-49930A, and JP H8-296908A. Specifically, according to JP H1-107071A, the bypass pipe is newly provided to the air conditioning system in addition to the inlet pipe and the outlet pipe of the accumulator. An optical liquid surface detection sensor is provided at the accumulator of the air conditioning systems in JP H4-222366A, JP H8-49930A, and JP H8-296908A.
A need exists for an air conditioning system and an accumulator which are not susceptible to the drawback mentioned above.
Further, a need exists for an air conditioning system using the two phase refrigerant, which promptly detects a liquid surface of the refrigerant in an accumulator with a simple configuration and contributes to improvement of an operation efficiency during the low temperature cooling operation.